Photoredox/Bismuth Relay Catalysis Enabling Reductive Alkylation of Nitroarenes with Aldehydes.

The effective transition metal-free photoredox/bismuth dual catalytic reductive dialkylation of nitroarenes with benzaldehydes has been reported. The nitroarene reduction through visible light-driven photoredox catalysis was integrated with subsequent reductive dialkylation of anilines under bismuth catalysis to enable the cascade reductive alkylation of nitroarenes with carbonyls. Salient features of this relay catalysis system include mild reaction conditions, no requirement for transition metal catalysts, easy handling, step-economy, and high selectivity.

Reduction-Specified Coupling Reactions of Nitroarenes by Heterogeneous Cobalt Catalysis.

The in-depth study on reduction-specified coupling reactions of the nitroarenes by heterogeneous cobalt catalysis opens a door for diversified syntheses of functional N-containing molecules. Guided by the structure-function relationship of heterogeneous materials, rational design of nano-catalysts can effectively regulate the routes of organic reactions. Precise transformation of the intermediates generated during the nitroarene reduction with a suitable nano-catalyst is a promising way to develop new tandem reactions, and to synthesize structurally novel compounds that are of difficult access with the conventional approaches.

Bimetallic nanoparticles supported on Ce-BTC for highly efficient and stable reduction of nitroarenes: Towards environmental sustainability.

The development of a catalyst with a consistent and clearly defined crystal structure is crucial for establishing an efficient catalytic performance system. This study focuses on catalyzing the reduction of nitroarenes to amino-derivatives in an aquatic environment at ambient temperature, employing metallic (Au) and bimetallic (Au-Pd or Au-Ag) nanoparticles loaded on a Ce-BTC metal-organic framework using a facile sol-immobilization approach. Diverse analytical instruments, comprising SEM, TEM, XRD, FT-IR, XPS, TGA, and N2 isotherm, have been utilized to characterize the synthesized catalysts. Among the catalysts that were fabricated, Au-Pd@Ce-BTC displayed the maximum catalytic efficacy, offering a rate constant (kapp) of 0.5841 min-1, conversion percentages reaching 99.7%, and a KAF of 116.8 min-1g-1. Moreover, it exhibited remarkable recyclability over five consecutive cycles. This catalyst offers the advantages of operating under ambient reaction conditions and exhibiting tolerance to a broad range of substrates containing various functional moieties. The mechanistic understanding of nitroarene reduction and the factors contributing to the superior activity of Au-Pd/Ce-BTC are explored through spectroscopic and porosity analyses. Spectroscopic measurements indicate that the elevated Auo and Pdo/Pd2+ ratio, increased surface area, and the synergistic collaboration of the bimetallic NPs are key factors contributing to the heightened activity of Au-Pd/Ce-BTC. These findings hold significant appeal from both an industrial and academic standpoint.

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods.

CeO2 nanorod based catalysts for the base-free synthesis of azoxy-aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (Ov ) and base sites are critical for their excellent catalytic properties. The Ov , i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α-Csp3 -H in ethanol to the nitro group coupling it to the redox reactions between Ce3+ and Ce4+ . At the same time, the base sites catalyze the condensation step to selectively produce azoxy-aromatics. The catalytic route opens a much improved way to use non-noble metal oxides without additives for the selective functional group reduction and coupling reactions.

Palladium-Catalyzed Reductive Double Carbonylation of Nitroarenes with Aryl Halides Using Mo(CO)6 as a Reductant and Carbonyl Source.

A new palladium-catalyzed reductive double carbonylation of nitroarenes with aryl halides for the synthesis of benzoxazin-4-ones has been reported. The key to success was the use of Mo(CO)6 as a reductant and bench-stable solid carbonyl sources. Various aryl iodides, bromides, and trifluoromethanesulfonates are suitable reaction partners and produce corresponding benzoxazin-4-one derivatives in moderate to good yields. Preliminary mechanistic studies indicate that nitrosoarene was first generated as the key intermediate through nitro reduction. Remarkably, this method avoids the use of toxic CO gas and is further applied to the late-stage modification of estrone.

Denitrative Hydroxylation of Unactivated Nitroarenes.

A one-step method for the conversion of nitroarenes into phenols under operationally simple, transition-metal-free conditions is described. This denitrative functionalization protocol provides a concise and economical alternative to conventional three-step synthetic sequences. Experimental and computational studies suggest that nitroarenes may be substituted by an electron-catalysed radical-nucleophilic substitution (SRN 1) chain mechanism.

Direct Synthesis of Unprotected Indolines Through Intramolecular sp3 C-H Amination Using Nitroarenes as Aryl Nitrene Precursors.

Given the prevalence of molecules containing nitro groups in organic synthesis, innovative methods to expand the reactivity of this functional group are of interest in both industrial and academic settings. In this report, a metal-free intramolecular benzylic sp3 C-H amination is disclosed using aryl nitro compounds as aryl nitrene precursors. Organosilicon reagent N,N'-bis(trimethylsilyl)-4,4'-bipyridinylidene (Si-DHBP) served as an efficient reductant in the transformation, enabling the in situ generation of aryl nitrene species for the direct, metal-free synthesis of unprotected 2-arylindolines from the corresponding nitroarene compounds.

Nano-sized and microporous palladium catalyst supported on modified chitosan/cigarette butt composite for treatment of environmental contaminants.

This study reports a versatile process for the fabrication of a microporous heterogeneous palladium nanocatalyst on a novel spherical, biodegradable, and chemically/physically resistant catalyst support consisting of chitosan (CS) and cigarette waste-derived activated carbon (CAC). The physicochemical properties of the microporous Pd-CS-CAC nanocatalyst developed were successfully determined by FTIR, XRD, FE-SEM, TEM, BET, and EDS techniques. TEM studies showed that the average particle size of the synthesized Pd NPs was about 30 nm. The catalytic prowess of microporous Pd-CS-CAC was evaluated in the reduction/decolorization of various nitroarenes (2-nitroaniline (2-NA), 4-nitroaniline (4-NA), 4-nitrophenol (4-NP), and 4-nitro-o-phenylenediamine (4-NPD)) and organic dyes (methyl red (MR), methyl orange (MO), methylene blue (MB), congo red (CR), and rhodamine B (RhB)) in an aqueous medium in the presence of NaBH4 as the reducing agent at room temperature. The catalytic activities were studied by UV-Vis absorption spectroscopy of the supernatant at regular time intervals. The short reaction times, mild reaction conditions, high efficiency (100% conversion), easy separation, and excellent chemical stability of the catalyst due to its heterogeneity and reusability are the advantages of this method. The results of the tests showed that reduction/decolorization reactions were successfully carried out within 10-140 s due to the good catalytic ability of Pd-CS-CAC. Moreover, Pd-CS-CAC was reused for 5 consecutive times with no loss of the initial shape, size, and morphology, confirming that it was a sustainable and robust nanocatalyst.

Analogy of the Reactions of Aromatic and Aliphatic π-Electrophiles with Nucleophiles.

The aim of this essay is to disclose the similarity of a great variety of reactions that proceed between nucleophiles and π-electrophiles-both aromatic and aliphatic. These reactions proceed via initial reversible addition, followed by a variety of transformations that are common for the adducts of both aliphatic and aromatic electrophiles. We hope that understanding of this analogy should help to expand the scope of the known reactions and inspire the search for new reactions that were overlooked.

Effective Synthesis of 4-Quinolones by Reductive Cyclization of 2'-Nitrochalcones Using Formic Acid as a CO Surrogate.

4-Quinolones are the structural elements of many pharmaceutically active compounds. Although several approaches are known for their synthesis, the introduction of an aryl ring in position 2 is problematic with most of them. The reductive cyclization of o-nitrochalcones by pressurized CO, catalyzed by ruthenium or palladium complexes, has been previously reported to be a viable synthetic strategy for this aim, but the need for pressurized CO lines and autoclaves has prevented its widespread use. In this paper, we describe the use of the formic acid/acetic anhydride mixture as a CO surrogate, which allows us to perform the reaction in a cheap and commercially available thick-walled glass tube without adding any gaseous reagent. The obtained yields are often high and compare favorably with those previously reported by the use of pressurized CO. The procedure was applied to a three-step synthesis from commercially available and cheap reagents of the alkaloid Graveoline.

Olefin Dihydroxylation Using Nitroarenes as Photoresponsive Oxidants.

Vicinal diols are abundant among natural and synthetic molecules, and also represent valuable intermediates throughout organic synthesis. Olefin dihydroxylation is an effective strategy to access these derivatives owing to the broad range and availability of alkene feedstocks. OsO4 is among the most used reagents to achieve this transformation, yet its high toxicity and cost remain concerning. Herein, we present a mechanistically distinct strategy for olefin dihydroxylation using nitroarenes as photoresponsive oxidants. Upon purple LEDs irradiation, these species undergo a [3+2]-photocycloaddition with a wide range of olefins to give stable 1,3,2-dioxazolidine intermediates. These species can be accumulated in solution and then reduced in situ to the desired diols, utilising readily accessible and easy to handle solid reagents as H2 surrogates.

Utilizing Nitroarenes and HCHO to Directly Construct Functional N-Heterocycles by Supported Cobalt/Amino Acid Relay Catalysis.

Due to the generation of multiple intermediates during the nitroarene reduction, precise interception of single one to develop tandem reactions involving both C-C and C-N bond formations still remains a significant challenge. Herein, the relay catalysis of a supported bifunctional cobalt catalyst with l-proline has been successfully applied to establish a bran-new reductive annulation reaction of nitroarenes and formaldehyde, which enables direct and diverse construction of both symmetrical and unsymmetrical 1,3-diaryl imidazolines. It proceeds with operational simplicity, good substrate and functionality compatibility, and excellent step and atom-efficiency. Mechanistic studies reveal that the Co-catalyst exhibits a synergistic effect on the formation of key N-hydroxy imine, and the l-proline subsequently facilitates the key C-C bond formation. The current work opens a door to develop useful transformations with nitroarenes by reduction-interrupted strategy.

Alkylation of Nitroarenes via Vicarious Nucleophilic Substitution - Experimental and DFT Mechanistic Studies.

Alkylation of nitroarenes via Vicarious Nucleophilic Substitution (VNS) was tested experimentally and modelled with DFT calculations. Mechanistic studies reveal intrinsic differences between reactions of archetypal carbanion precursor PhSO2 CH2 Cl, and alkyl phenyl sulfones, in which benzenesulfinate acts as a leaving group. Accordingly, for the latter precursors steric hindrance develops at the ß-elimination step, that raises energy barrier and results in the formation of byproducts.

Oxidative Cleavage of Alkenes by Photosensitized Nitroarenes

This article highlights the recent seminal findings on the possibility to use photoexcited nitroarenes as modular and easily dosable reagents which can mimic the reactivity of ozonolysis for the oxidative conversion of alkenyl bonds into carbonyl groups in a highly selective fashion.

An Adaptive Rhodium Catalyst to Control the Hydrogenation Network of Nitroarenes.

An adaptive catalytic system that provides control over the nitroarene hydrogenation network to prepare a wide range of aniline and hydroxylamine derivatives is presented. This system takes advantage of a delicate interplay between a rhodium(III) center and a Lewis acidic borane introduced in the secondary coordination sphere of the metal. The high chemoselectivity of the catalyst in the presence of various potentially vulnerable functional groups and its readiness to be deployed at a preparative scale illustrate its practicality. Mechanistic studies and density functional theory (DFT) methods were used to shed light on the mode of functioning of the catalyst and elucidate the origin of adaptivity. The competition for interaction with boron between a solvent molecule and a substrate was found crucial for adaptivity. When operating in THF, the reduction network stops at the hydroxylamine platform, whereas the reaction can be directed to the aniline platform in toluene.

CoPd Nanoalloys with Metal-Organic Framework as Template for Both N-Doped Carbon and Cobalt Precursor: Efficient and Robust Catalysts for Hydrogenation Reactions.

In this work, a series of metal-organic framework (MOF)-derived CoPd nanoalloys have been prepared. The nanocatalysts exhibited excellent activities in the hydrogenation of nitroarenes and alkenes in green solvent (ethanol/water) under mild conditions (H2 balloon, room temperature). Using ZIF-67 as template for both carbon matrix and cobalt precursor coating with a mesoporous SiO2 layer, the catalyst CoPd/NC@SiO2 was smoothly constructed. Catalytic results revealed a synergistic effect between Co and Pd components in the hydrogenation process due to the enhanced electron density. The mesoporous SiO2 shell effectively prevented the sintering of hollow carbon and metal NPs at high temperature, furnishing the well-dispersed nanoalloy catalysts and better catalytic performance. Moreover, the catalyst was durable and showed negligible activity decay in recycling and scale-up experiments, providing a mild and highly efficient way to access amines and arenes.

Novel aminoarylcysteine adducts in globin of rats dosed with naphthylamine and nitronaphthalene isomers.

Novel aminonaphthylcysteine (ANC) adducts, formed via naphthylnitrenium ions and/or their metabolic precursors in the biotransformation of naphthylamines (NA) and nitronaphthalenes (NN), were identified and quantified in globin of rats dosed intraperitoneally with 0.16 mmol/kg b.w. of 1-NA, 1-NN, 2-NA and 2-NN. Using HPLC-ESI-MS2 analysis of the globin hydrolysates, S-(1-amino-2-naphthyl)cysteine (1A2NC) together with S-(4-amino-1-naphthyl)cysteine (4A1NC) were found in rats given 1-NA or 1-NN, and S-(2-amino-1-naphthyl)cysteine (2A1NC) in those given 2-NA or 2-NN. The highest level of ANC was produced by the most mutagenic and carcinogenic isomer 2-NA (35.8 ± 5.4 nmol/g globin). The ratio of ANC adduct levels for 1-NA, 1-NN, 2-NA and 2-NN was 1:2:100:3, respectively. Notably, the ratio of 1A2NC:4A1NC in globin of rats dosed with 1-NA and 1-NN differed significantly (2:98 versus 16:84 respectively), indicating differences in mechanism of the adduct formation. Moreover, aminonaphthylmercapturic acids, formed via conjugation of naphthylnitrenium ions and/or their metabolic precursors with glutathione, were identified in the rat urine. Their amounts excreted after dosing rats with 1-NA, 1-NN, 2-NA and 2-NN were in the ratio 1:100:40:2, respectively. For all four compounds tested, haemoglobin binding index for ANC was several-fold higher than that for the sulphinamide adducts, generated via nitrosoarene metabolites. Due to involvement of electrophilic intermediates in their formation, ANC adducts in globin may become toxicologically more relevant biomarkers of cumulative exposure to carcinogenic or non-carcinogenic arylamines and nitroarenes than the currently used sulphinamide adducts.

Selective and Additive-Free Hydrogenation of Nitroarenes Mediated by a DMSO-Tagged Molecular Cobalt Corrole Catalyst.

We report on the first cobalt corrole that effectively mediates the homogeneous hydrogenation of structurally diverse nitroarenes to afford the corresponding amines. The given catalyst is easily assembled prior to use from 4-tert-butylbenzaldehyde and pyrrole followed by metalation of the resulting corrole macrocycle with cobalt(II) acetate. The thus-prepared complex is self-contained in that the hydrogenation protocol is free from the requirement for adding any auxiliary reagent to elicit the catalytic activity of the applied metal complex. Moreover, a containment system is not required for the assembly of the hydrogenation reaction set-up as both the autoclave and the reaction vessels are readily charged under a regular laboratory atmosphere.

Preparation and Application of a Hydrochar-Based Palladium Nanocatalyst for the Reduction of Nitroarenes.

In the present study, a novel heterogeneous catalyst was successfully fabricated through the decoration of palladium nanoparticles on the surface of designed Fe3O4-coffee waste composite (Pd-Fe3O4-CWH) for the catalytic reduction of nitroarenes. Various characterization techniques such as XRD, FE-SEM and EDS were used to establish its nano-sized chemical structure. It was determined that Pd-Fe3O4-CWH is a useful nanocatalyst, which can efficiently reduce various nitroarenes, including 4-nitrobenzoic acid (4-NBA), 4-nitroaniline (4-NA), 4-nitro-o-phenylenediamine (4-NPD), 2-nitroaniline (2-NA) and 3-nitroanisole (3-NAS), using NaBH4 in aqueous media and ambient conditions. Catalytic reactions were monitored with the help of high-performance liquid chromatography. Additionally, Pd-Fe3O4-CWH was proved to be a reusable catalyst by maintaining its catalytic activity through six successive runs. Moreover, the nanocatalyst displayed a superior catalytic performance compared to other catalysts by providing a shorter reaction time to complete the reduction in nitroarenes.

Light-Promoted C-N Coupling of Aryl Halides with Nitroarenes.

A photochemical C-N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step-economic extension to the widely used Buchwald-Hartwig C-N coupling reaction. The method tolerates coupling partners with steric-congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI /NiIII cycle, to a nitrosoarene intermediate.